Various methods are known for the processing and clean up of organic wastes, solids, semi-solids and liquids, to produce non-hazardous products for release to the environment. These include the known techniques of fermentation which includes both aerobic and anaerobic digestion processes, and processes which employ steps encompassing both aerobic and anaerobic digestion. The objective of both is to reduce, as well as to efficiently and effectively stabilize sludge solids, and produce clean effluents for discharge to the environment, e.g., to a natural stream. Anaerobic digestion generally offers advantages over aerobic digestion in that methane is produced, the methane being suitable as a fuel gas which can be used internally to supply process heat, as well as provide process credits for external use. Anaerobic digestion of organic wastes also generally produces less sludge than aerobic digestion. This is because the aerobic microorganisms' waste is about 85 percent of what is consumed by the microorganisms. On the other hand, however, anaerobic processes generally require longer periods of time for the effective clean up and stabilization of solids, and the production of clean effluents. Generally from about 20 to 30 days of anaerobic fermentation is required at ambient temperatures, as commonly practiced, to produce a reasonably stable form of solids, and effluent suitable for direct discharge to the environment. By warming the fermentation mixture this period has been reduced, ideally to about 12 to 20 days. (Reference is made to Union Carbide's U.S. Pat. No. 4,246,099 which issued to Gould et al on Jan. 20, 1981. This reference provides a historical perspective on anaerobic and aerobic digestion).
Anaerobic digesters are constituted generally as closed or domed vessels within which very large charges of organic waste are maintained, and fermented in batch. Anaerobic digestion of the waste produces methane gas and generally, after about 20-30 days, the liquid and suspended solids component are withdrawn into a separator and separated into liquid and slurry components. The slurry component is generally sufficiently stabilized that it is suitable as a land fill, and the liquid sufficiently clean for discharge to a natural stream. Whereas anaerobic digesters have proven useful for handling large volumes of municipal and industrial wastes, the time required for digestion of the organic waste is entirely too long. Consequently, most often aerobic digesters are employed in handling large volumes of municipal and industrial wastes. Both aerobic and anaerobic digesters however are unsuitable for handling small volumes of organic wastes. There is today a pressing need for improved processes, and digesters capable of processingsmall volumes of organic wastes over shorter periods of time. Albeit anaerobic processes, and digesters, offer certain advantages, the time period required for adequate effective fermentation militates against their use.